Project Summary/Abstract: This proposal describes a five-year career development program designed to support an academic, physician- scientist career. The proposed research project will capitalize on the expertise and resources available at Washington University School of Medicine, which has a strong tradition of developing physician-scientists. Dr. Timothy Ley, an expert in cancer genomics and epigenetics, and a recipient of multiple mentorship awards nationally and at Washington University, will serve as the primary research mentor. The ultimate goal of the candidate is to be an independent investigator in an academic medical center, studying epigenetic control of cutaneous carcinogenesis, and caring for patients with cutaneous malignancies. The long-term goal of this study is to define alterations in the epigenetic ?state? of epidermal keratinocytes that arise during normal aging and their roles in creating age-related susceptibilities for skin cancer. Increasing age and UV light exposure are the two most prominent epidemiologic risk factors for the development of skin cancer in fair skinned populations. Recent studies have identified clonal expansions of cells harboring oncogenic mutations from clinically normal skin, suggesting that additional genetic or epigenetic events are required for transformation to skin cancer. Aging and UV light exposure not only cause DNA damage and mutations, but also have been demonstrated to cause DNA methylation changes in the skin of human patients; whether these alterations are relevant for skin cancer pathogenesis is currently unknown. Our preliminary data suggests that the DNA methylation state of epidermal cells undergoes a programmed change at specific loci in mice as they age, as do stereotypical changes in gene expression resulting in the development of a population of cells that we have named ?basal aging-signature keratinocytes? (BASKs). We will explore the hypothesis that age-related epigenetic changes, including DNA methylation, may increase susceptibility to skin cancer development with the following specific aims: Aim 1: We will define the epigenetic events in murine epidermis that result from normal aging, relate them to functional changes, and assess their roles in the development of skin cancers. We will define the epigenetic changes in BASK cells, define biomarkers that allow for the purification of this population, and test the susceptibility of aged skin to KRASG12D- mediated skin tumorigenesis and the development of UVB-induced, mutated Trp53 clonal islands in the skin. Aim 2: We will define the roles of individual DNA methyltransferases for the development of age-dependent methylation states and for the neoplastic transformation of skin. Using mice conditionally deficient in Dnmt1, Dnmt3a, and/or Dnmt3b in epidermal cells, we will determine whether these enzymes contribute to age-related development of the BASK phenotype, and whether their deficiencies are relevant for KRASG12D-mediated skin tumorigenesis. If successful, insights gained from this work may allow for the creation of novel therapeutic or preventative approaches for the keratinocyte cancers, basal cell and squamous cell carcinoma.